Electronic tube circuit



March 18, 1941. a. H. PQALMA Er AL 2,235,190

ELECTRONIC CIRCUIT 7 Filed March 9, 1938 INVENTORS GERR/T H. P. ALMA JOHAN L. H. JON/(ER.

BY g

Mm, ATTORNEY n r x nnscriio'hiio TUBE oiaouir J Ge'rrit Hendrik letrusAlma and Johan-,Lodewijk i Hendrik Jonker,Eindhoven, Netherlands, as-

,. signor, by mesne' assignments, to Radio G0rpo-' ration ofiAmerica, New York,-N;:Y., a corpora tionof Delaware Application March 9,

1938, Serial No. 194,788

In the Netherlands March 10, 1937 2 Claims.

This invention relates to a circuit arrangement comprising a discharge tube having at least a cathode, a control grid, an anode and an auxiliary cathode which is either made from or coated with a material emitting secondary electrons under bombardment by electrons.

The invention envisages a circuit arrangement by means of which the feed voltages required for the different electrodes, more particularly for the auxiliary cathode, can be obtained in a simple manner.

According to the invention the auxiliary cathode is connected'for this purpose to a point of a potentiometer connected between a point having a positive potential and the cathode, the portion of the potentiometer between the auxiliary cathode and the cathode being small with respect to the remainder of the potentiometer.

The common part of the conductors for the cathode and the auxiliary cathode preferably include a resistance which lies at the same time in the control grid circuit of the discharge tube, in order to obtain the required control grid bias.

The invention will be more clearly understood by reference to the accompanying drawing representing, by way of example, one embodiment thereof.

This drawing shows a discharge tube I comprising a cathode 2, which emits electrons upon being heated, a control grid 3, a screen grid 4, an anode 6 and an auxiliary cathode 5 which emits secondary electrons under bombardment by electrons. The positive bias of the screen grid 4 and of the anode 6 are taken off from a voltage source (not represented), whose positive terminal is connected to a terminal I, whereas the negative terminal is connected to a terminal 8. Between the terminals 1 and 8 is provided a potentiometer 9 from which the screen grid voltage is taken off. The voltage between the terminals I and 8 may, for instance, have a value of 250 volts, whilst the screen grid is connected to a point having, for instance a tension of about 150 volts relatively to d theterminal 8. According to the invention, the

part of the total voltage available between the terminals 1 and 8. Due to this the auxiliary cathode 5 initially has a potential of, say about 40 volts relatively to the cathode. Part of the electrons emitted by the cathode 2 will reach the 5 auxiliary cathode 5 and dislodge therefrom a larger number of secondary electrons. Owing to this the resistance II is traversed by a current directed from the auxiliary cathode 5 to the cathode 2, which results in that the auxiliary cathode 10 5 becomes more positive relatively to the cathode 2. Due -to this a larger number of primary electrons will reach the auxiliary cathode 5 so that the current traversing the resistance II increases and the voltage of the auxiliary cathode 5 increases further until a state of equilibrium is finally reached, in which the auxiliary cathode 5 has a much higher voltage than in the beginning relatively to the cathode 2.

The bias of the control grid 3 is obtained by means of a resistance I2 which is shunted by a condenser and interposed in the common part of the leads to the cathode and the auxiliary cathode of the tube I, due to which the current of the auxiliary cathode 5 also flows through the resistance I2 and the desired grid bias can be obtained at a much smaller value of the resistance I2.

The control grid 3 of the tube I is preferably connected to a point l3 of the potentiometer 9 which point has a positive voltage of, say, 4 volts with respect to the terminal 8, due to which better stabilization of the anode current is ensured. In fact, the discharge tube I has a very high mutual conductance so that a slight variation of the control grid bias involves a great variation of the anode current. As is well known a resistance interposed in the cathode lead of a discharge tube has a stabilizing efiect on the anode current, since an increase of anode current is accompanied by an increase of the grid bias in a negative sense.

It has now been found that a more efficient stabilization of the anode current can be obtained by connecting the control grid to the positive terminal of a source of direct voltage inserted, in series with the said resistance in the control grid circuit. In the arrangement illustrated the said supply is constituted by the bottom part of the potentiometer 9.

We claim:

1. In signalling apparatus, an electronic tube provided with a cathode, a control grid, an anode and an auxiliary cathode capable of emitting electrons when subjected to electronic bombardment, said auxiliary cathode being positioned relative 55 to the other electrodes of said tube so as to intercept at least a portion of the electrons emitted by the cathode, and said anode being in such a position relative to the auxiliary cathode as to attract secondary electrons from said auxiliary cathode, a source of" direct current voltage having a positive terminal and a negative terminal, a potentiometer resistance connected between said two terminals, a connection including a resistance element between the cathode and said negative terminal, a connection between the anodeand said positive terminal, means for connecting the control grid to a point of said potentiometer resistance which in the operation of said apparatus is slightly positive with respect to the negative terminal, a circuit including a pair of resistors in 'of said auxiliary electrode to a point of the potentiometer resistance connected between the two terminals which is near the positive terminal.

GERRIT -HENDRIK PE'I'RUS ALMA. J OHAN LODEWIJK HENDRIK J ONKER. 

